Split gate non-volatile memory cells with three gates are known. See for example U.S. Pat. No. 7,315,056, which discloses split gate memory cells each having source and drain regions in a semiconductor substrate with a channel region extending there between, a floating gate over a first portion of the channel region, a control gate (also called a word line gate) over a second portion of the channel region, and a P/E gate over the source region.
Fabrication method improvements are needed to better control the formation of various elements of the memory cells.